A large proportion of the world's population does not have access to a consistent and reliable supply of mains electricity. Underdeveloped countries, or regions remote from populated areas, frequently suffer from rationing of electrical power, often implemented by means of “load shedding”, being the creation of intentional power outages, or failures of the distribution network.
The storage of vaccines, food items and beverages at appropriate temperatures is difficult in such areas where this absence of a constant and/or reliable supply of electrical power restricts the widespread use of conventional refrigeration equipment. Vaccines, for example, are required to be stored within a narrow temperature range between approximately 2-8° C., outside of which their viability can be compromised or destroyed. Similar problems arise in connection with the storage of food, particularly perishable food items, and packaged beverages such as canned or bottled drinks.
In response to this problem, the present applicants have previously proposed a form of refrigeration apparatus, disclosed in international patent application no. PCT/GB2010/051129, which permits a refrigerated storage space to be maintained within a temperature range of 4-8° C. for up to 30 days following a loss of electrical power. This prior art apparatus comprises a payload space for vaccines, food items, drinks containers or any other item to be cooled, the payload space being disposed at a lower region of a thermally insulated reservoir of water. Above the reservoir, and in fluid communication therewith, a water-filled head space containing a cooling element or low-temperature thermal mass, provides a supply of cold water to the reservoir.
This prior art apparatus relies upon the known property that water is at its maximum density at approximately 4° C. Thus, water cooled to this temperature by the cooling element or thermal mass in the head space tends to sink down into the reservoir, settling at the lower region surrounding the payload space which, through thermal transfer, is cooled to a temperature at or close to 4° C.
The applicants have identified a need to improve on the above mentioned apparatus to facilitate packaging, transportation and efficiency in some applications. It is against this background that the present invention has been conceived. Other aims and advantages of the invention will become apparent from the following description, claims and drawings.